The subject of the present invention is a speed-increasing device for the rotary driving mechanism of a tool fixed in the head of an angle-drive used in dentistry, of the type which consists of a shaft which is driven directly by the driving shaft on which the angle-drive is arranged, and the said shaft meshes at its end with a first pinion of an inclined shaft, the said inclined shaft carrying a second pinion at its other end.
Speed-increasing angle-drives of this type have been known for a long time. In systems of the prior art, the said second pinion of the inclined shaft meshes directly with the pinion on the head spindle of the angle-drive.
In these devices, the pinion on the shaft driven by the motor turns at about 40,000 revolutions per minute.
The inclined shaft turns at about 80,000 revolutions per minute which gives the tool a speed of rotation of 120,000 revolutions per minute.
It is now desired to achieve higher head speeds, of the order of 160,000 revolutions per minute.
With known devices, this may only be obtained with an inclined shaft turning at 120,000 revolutions per minute. This is excessive for the moving parts concerned, and results in unbalance and vibration.